The program is subdivided into three projects plus administrative core support through the Institute of Arctic Biology. The three projects are: I. Hibernation and Hypothermia in Arctic Mammals. The objectives are to understand the physiological and biochemical mechanisms which enable animals to utilize hibernation or hypothermia as a means of survival through studies on the regulation of carbohydrate metabolism and the control of rate limiting enzymes of intermediary metabolism. Comparisons are made between non-hibernating and hibernating mammals and poikilotherms to elucidate the differences which limit the tolerance of hypothermia in other mammals. II. Metabolism and Thermoregulation in Cold Climates. The objectives are to study (1) the role of substrates (i.e. carbohydrate, lipid) and their mobilization and control by neuroendocrine mechanisms in metabolic responses to cold and maximum metabolism, (2) the importance of body water conservation in thermoregulation and to survival and (3) neonatal mechanisms of cold resistance in arctic homeotherms. III. Nutrition in Northern Populations. The objectives include studies on nutritional strategies adopted by arctic animals for combating cold stress and surviving the arctic winter through estimation of rates of whole animal lipogenesis, establishment of techniques for estimating endogenous rates of lipogenesis through use of tritium in large and small herbivores and carnivores, determination of the effect of cold adaptation and nutrition on carbohydrate and lipid storage in small mammals and analysis of the tissue lipid essential and non-essential fatty acids of arctic animals to understand mechanisms resulting in specific fatty acid compositions.